This invention relates to coated elements, to coating processes used in the manufacture of coated elements, and to surfactant coating compositions useful as coating aids in such processes. More particularly, the present invention relates to the use of a surfactant coating composition which can be uniformly applied as a coating aid layer upon a contiguous layer, such as a gelatin-containing coating layer also containing an anionic surfactant, for example a layer of a radiation sensitive film element to facilitate manufacture of the element, while also providing the resulting surfactant coated surface of the element with improved protection against development of electrical charge.
Many image-recording systems use image-forming materials comprising a support such as glass, metal, paper or plastic, overcoated with one or more layers comprising hydrophilic colloidal materials such as gelatin, at least some of which layers contain one or more materials that are sensitive to radiation. The best known of the image-recording systems utilizes silver salt(s) as the sensitive material. However, a wide variety of other materials are sensitive to radiation (reacting in a desired manner upon exposure to radiation) including certain unsaturated polymers and non-silver photographic systems. In image-recording systems, the layer containing the radiation sensitive material is frequently used in combination with several other layers of various coatings which are applied in a plurality of coatings on one surface or the other or both surfaces of a base or support, and which serve, for example, as carriers for reflective pigments, antihalation pigments or dyes, or filter dyes, or as undercoatings to improve adhesion and coatings to impart abrasion resistance, and the like. Other systems for other purposes using a plurality of layers similarly also are known.
In the deposition of coating compositions for the formation of contiguous coatings, or layers, particularly those containing gelatin, it has been customary to employ surface active agents as coating aids in the coating compositions to improve the quality and uniformity of the layers, and to improve the ease and reproductibility of their application. While the use of surfactants in this way can improve the properties of a particular deposited, or coated, layer, they can also adversely affect the characteristics of the element, for example, by causing surface variations, repellency between substrate layers, "pulling in" of coatings from the edges of the film, permeability to processing solutions, and the like. For example, the presence of certain surfactants in an earlier-applied layer of coating can deleteriously affect the surface characteristics of a later-applied layer of coating, when the layers are contiguous layers, as in a coated silver halide emulsion layer, thereby making it extremely difficult to apply the later-applied layer of coating without defects even if a surfactant coating aid is present in the later-applied layer.
An example of a particularly troublesome situation is that which results when one applies a conventional radiation sensitive coating composition comprising, for example, water, a photographic dye, silver halide, gelatin and an anionic surfactant such as a sodium alkylaryl sulfonate (in appropriate amounts) to a support material, such as a conventional gelatin-subbed cellulose acetate film, or a subbed polyester photographic film support, forming on the gelatin containing layer a layer of radiation sensitive coating having a highly surface active surface, and one then attempts substantially simultaneously to overcoat upon such surface of the coating, at high production machine rates of several hundred feet per minute, a protective layer of gelatin, for example, from an aqueous cationic or nonionic surfactant-containing overcoating composition. It is found that one obtains an overcoated radiation sensitive element having many surface defects, such as repellency, pulled in edges, crescents, and the like, even though one or more conventional surfactants are used in the aqueous overcoating composition in an attempt to solve such coating difficulties.
Another serious problem which arises in the manufacture and use of polymeric film products, and especially of radiation sensitized (radiographic or photographic) materials, is the generation of static electrical charge. In the case of such sensitized goods, serious deleterious effects are produced when accumulated electrical charges discharge, producing light and/or "noise," (which is recorded as an image on photosensitive materials and as static on other materials, such as magnetic tape, that are sensitized to other specific, non-visible electromagnetic irradiations). Such discharge may occur in the course of manufacturing processes, such as coating, finishing or packaging, or it may occur during use of the finished product in cameras, printers, tape players and other associated equipment. Another less obvious deleterious effect which results from accumulation of charge on polymeric supports, coated or uncoated, in the manufacturing operation, is the production of coating defects such as "core mottle" and "roll convolution repeat", both of which are well known to those involved in the manufacture of these types of materials. Both of these undesirable effects are due to the uncontrolled, undesirable build-up of localized electrically charged areas on, or in the various products, in the course of the film manufacturing operation. These areas of localized charge give rise to nonuniformity in the overlying sensitized coatings during their application and combine with the above-discussed problems arising from surfactant use to create additional problems.
The Prior Art
One conventional type of surfactant that is well known for its surprisingly good ability as a coating aid is the nonionic type termed "alkylphenoxy poly(propylene oxide)" materials having the formula: ##SPC1##
wherein R.sub.5 is an alkyl group and contains from 6 to 18 carbon atoms, R.sub.6 is hydrogen or an alkyl group of from 1 to 18 carbon atoms, and Q is a polyether group comprising an average of from about 3 to about 15 units derived from glycidol (hydroxypropylene oxide), and the polyether group comprises n-propylene and isopropylene moieties. (Such nonionic materials are described in detail in U.S. Pat. 3,514,293 issued to Knox. The disclosure of the Knox patent is hereby incorporated by reference into the present patent application). However, on certain highly surface active layers, such as that described above, even the use of the Knox invention has not proved to be entirely satisfactory. The same can be said, in terms of varying degrees of non-success, for many other surfactants that are ordinarily utilized as coating aids in the manufacture of coated film elements, particularly radiation sensitive elements. Other prior art will be discussed herein where reference thereto is pertinent.